Proximity current detector



United States Patent 3,397,348 PROXIMITY CURRENT DETECTOR Raymond W.Hoeppel, P.0. Box 5,

Oak View, Calif. 93022 Continuation-impart of application Ser. No.219,602, Aug. 27, 1962. This application May 16, 1966, Ser.

6 Claims. (Cl. 317123) ABSTRACT OF THE DISCLOSURE An instrument fordetecting and measuring current flowing through a nearby wire comprisesa magnetically biased vibrating reed relay having a capacitor to retardits rate of vibration. The current flow is detected or measured by atransducer that is switched by the vibrating contacts of the relay, thevibration rate varying with the amount of current flowing through thewire.

This is a continuation-in-part of US. Patent No. 3,252,- 057 filed Aug.27, 1962.

This invention relates to a device for detecting the presence of currentflowing in a Wire without direct connections to the Wire, and moreparticularly to a magnetic current detector employing a novel type ofvibrating reed switch.

Current detectors in use today usually require direct connection to awire, and where a direct connection is not required, they are either lowin sensitivity or require complicated circuitry involving amplifiers.Also they usually dissipate power while in standby condition.

One object of this invention, therefore, is to provide a proximitycurrent detector that is very simple in construction and inexpensive,while at the same time being very sensitive to small current flow in anisolated wire.

Another object is to provide a current detector that will operate onsmall amounts of power and will not necessarily use power while instandby alert condition.

Another object is to provide a current detector that may be adjusted toproduce a control or warning action when the current falls below orrises above a predetermined value.

FIGURE 1 shows in cross section a current detector employing a slowrelease relay for control purposes, and using a current-carryingsolenoid as a bias source.

FIGURE 2 shows in cross section a current sensor using a permanentmagnet as a bias source and employing a loudspeaker as an audibleindicator of the status of the current, and an ammeter as a currentreadout device.

The basic detecting element in the current detector of this invention isthe sensitive vibrating reed switch described more fully in US. PatentNo. 3,252,057.

One form of such vibrating switch is shown in the device of FIGURE 1.Here a conventional double thro-w magnetic reed switch is connected withits normally closed contacts, 2 and 3, controlling a current in solenoid5, the current being provided by power source 7. Switch 2 is mountedwithin solenoid 5. When current flows through solenoid 5 the normallyclosed contacts, 2 and 3, open and the normally open contacts, 2 and 4,close because of the magnetic field created by the solenoid. Whencontacts 2 and 3 open, current ceases to flow through the solenoid andthese contacts again close by spring bias because of the collapse of themagnetic field. The process is thus repeated causing a vibration to beset up in the switch as long as power is supplied to the circuit. Acapacitor, 8, is shunted across the solenoid to stabilize the vibrationof the switch and to reduce its frequency of vibration. Relay 9 is aslow release relay in the vibrating circuit to produce steady stateswitching. It keeps contacts 9A and 913 closed as long as the switch isvibrating and these contacts may be used for signalling or controlpurposes.

Now if a regulated, steady current is applied to solenoid 5 by means ofpower source 10 and variable resistor 11, an additional flux will becreated in the vicinity of the vibrating switch causing a steady,magnetic biasing action on the switch. If this bias flux opposes thatproduced by the intermittant current from power source 7, then thefrequency of vibration of the switch will increase. If this biasre-inforces that produced by the intermittent current the frequency ofvibration will be lessened until at some value of current in the biascircuit, vibration will cease entirely. At that point, a slight increasein bias of the proper polarity will initiate vibration, or a slightincrease in flux from any other external flux source of the properpolarity will initiate vibration. Hence if the switch is on the verge ofvibration and is placed near a conductor carrying a current in suchdirection that it produces a flux at the switch that opposes the biasflux, then vibration will start when this current flows. In FIGURE 1provision is made for the placement of a conductor 6, carrying acurrent, in a fixed position with respect to the switch. Conductor 6 isshown in the position 'where it is most effective in operating theswitch but if the current through the Wire is sufiiciently high, theconductor may be placed further away, but usually in a positiongenerally transverse to the major axis of the switch.

Another method of lessening the sensitivity of the detector is byincreasing the bias. Thus the switch may be adjusted to start to vibrateat a wide range of currents carried by the conductor, and in this mannermay serve as an overload detector with a variable set point, which isattained by manual adjustment of variable resistor 11.

The switch will respond to either direct or alternating current flowingthrough the conductor, 6, with currents as low as 0.1 ampere beingreadily detected.

The detector of FIGURE 1 can also be used to indicate a drop in currentflowing through conductor 6. This is accomplished by adjusting the bias,by means of resistor 11, 'while current is flowing through conductor 6so that the switch just stops vibrating. The current flowing throughconductor 6 must be of such polarity that it produces a flux thatreinforces the bias flux. Then when there is a decrease in the currentthe switch will be set in vibration, causing relay 9 to close contacts9A and 9B.

In FIGURE 2 is shown another embodiment of the invention wherein thebias flux is produced by a permanent magnet instead of by solenoid, andadjustment of bias is attained by moving the magnet with respect to theswitch. In this embodiment the normally open contacts of the reed switchare used for switching instead of the normally closed contacts as inFIGURE 1, thus necessitating a different polarity in biasing than in thefirst device.

In FIGURE 2, a conventional, normally open magnetic reed switch ishoused within solenoid 1S, and as before the switch contacts, 13 and 14,are connected in series with solenoid 15 and power source 23. Inaddition, an ammeter, A, and a loudspeaker, 24 are in this same seriescircuit. A capacitor, 16, shunts the solenoid. The vibrating switchassembly is housed within container 17, by means of a potting compound,18, although other methods of housing can be used. Screw 22 is threadedinto the top of container 17 and a permanent magnet, 21 is attached tothe end of the screw. A slot, 19, cut into the side of the containerserves to accommodate conductor 20, through which passes the current tobe detected.

Before the switch of FIGURE 2 can be set into vibration, contacts 13 and14 must first be biased to a closed position by means of permanentmagnet 21. Current will then flow through these contacts, the solenoid,the ammeter and the loudspeaker, and this current must produce a flux atthe switch that opposes that of the bias magnet. When the current flows,the flux produced by the solenoid causes the contacts, 13 and 14 toopen,thus stopping this current fiow whereupon they are closed again bythe bias force. Thiscycle is repeated as long as power is applied to thecircuit, setting up :a vibration in the switch contacts and causing asound to issue from the loudspeaker. After the switch has been set intovibration the frequency of vibration will be related to the bias fluxproduced by magnet 21, the frequency increasing as this flux isincreased and decreasing if this bias is decreased, such as by movingmagnet 21 further away from the switch by means of screw 22. At somedefinite value of bias flux, vibration will stop, and then anyincreasein .bias flux will initiate vibration.

If the switch-is not vibrating and is on, the verge of vibration, thepassage of a small amount of current through conductor 20 will startvibration provided the fiuxproduced by this current reinforces the biasflux.

Then as the current in conductor 20 is increased, the frequency ofvibration will increase and the current passing through the ammeter, A,will increase proportionately. Thus by referring to the ammeter reading,a measure of the amount of current flowing through the conductor, 20will be attained. Hence the amount of current flow in conductor 20 maybe ascertained by listening to the pitch of the sound issuing from theloudspeaker or by reading the ammeter. Other forms of electromechanicaltransducers may be controlled by the vibrating switch contacts, such asfrequency sensitive relays, slow release relays, solid state relays andthe like.

It is obvious that the device of FIGURE 1 can be biased by permanentmagnets and that of FIGURE 2 can be biased by solenoid runs, such as isshown in FIGURE 1. Both types of biasing may be used in one detector,and more than one magnet is often used to enable more criticaladjustment of the bias flux. Either device in FIGURES 1 and 2 may beused for switching any of the various electromechanical transducersdiscussed. The device of FIGURE 1 may perform this switching either bycontacts 2 and 3 or by contacts 2 and 4. Either detector will senseeither alternating or direct current flowing through the conductor, andeither may be used to sense overload or underload currents by proper.adjustment of the amount and polarity of the bias, as has beenpreviously described. The bias produced by a permanent magnet can bevaried by moving the magnet in any direction with respect to the switcheither in linear or rotational fashion. The switches need not be housedin the operating solenoids as long as they are in flux couplingrelationship with the solenoids. The bias solenoid need not be integralwith the operating solenoid as in FIGURE 1, but can be a separatelywound coil.

I -'--Although this invention is described by means-of embodiments shownin the drawings, yet various modifications can, of course, be madewithout departing from the scope of the following claims. 5 What isclaimedis:

1. A current detector for detecting the flow of current in anisolatedfwire without connections thereto, said detectorcomprising incombination? a vibrating switch assembly ,comprisingin'cornbination anoperating solenoid, amagnetic reed switch in flux coupling relationshipwith said operating solenoid, Said, switch comprising at least twoferromagnetic reed contacts, said contacts being responsive to amagnetic field, said switch controlling a current throughsaid solenoid,means to connect a power source with said switch and solenoid,capacitive means connected in'circuit with said switch and solenoid tostabilizeuthe vibration 'ofsaid switch, and a source of constantmagnetic bias in flux coupling relationship with said switch,electromagnetic means responsive to said magnetic reed switch totranslate the vibration of said switch'into a mechanical displacement;and means to mount said vibrating switch assembly in a fixed positionwith respect to a conductor carrying an electric current, said assemblybeing located in such position that said switch is in flux couplingrelationship with the electromagnetic field emanating from saidconductor.

2. A currentdetector according to claim 1 wherein said reed switchcomprises at least two normally open contacts and at least two normallyclosed contacts and said normally closed contacts control the currentthrough said solenoid.

3. A current detector according to claim 1 wherein said source ofconstant magnetic bias comprises at least one permanent magnet, saidmagnet being located in a fixed position with respect to said switch.

4. A current detector according to claim 3 wherein the position of saidmagnet with respect to said switch is manually adjustable.

5. A current detector according to claim 1 where said source of constantmagnetic bias comprises a bias solenoid carrying a constant current.

6. A current detector according to claim 5 including means to manuallyvary the amount of said current flowing through said bias solenoid.

References Cited UNITED STATES PATENTS 2,073,913 I 3/1937 Wigan 335-87 X2,550,605 4/1951 Schenck 335-87 X 3,227,838 1/1966 Hoeppel 335- 1533,251,961 5/1966 Wintriss 335-151 X 3,264,423 8/1966 Mejean et al. 335-153 LEE T. HIX, Primary Examiner.

J. A. 'SILVERMAN, Assistant Examiner.

